Implement captcha check, don't reject entries yet.

Report if captcha check failed but accept entry anyway.

src/cgi.cpp

@@ -27,6 +27,7 @@
 #include <unicode/unistr.h>
 
 #include <algorithm>
+#include <array>
 #include <chrono>
 #include <cstdint>
 #include <fstream>
@@ -68,6 +69,13 @@ entry_type parse_formdata()
         throw SpamException{};
     }
 
+    if (!captcha_valid(static_cast<std::uint8_t>(std::stoul(cgi("captcha_id"))),
+                       cgi("captcha_answer")))
+    {
+        // throw CaptchaException{};
+        std::cout << "DEBUG: Captcha invalid. You can ignore this line.\r\n";
+    }
+
     entry.instance = cgi("instance");
     entry.tags = string_to_vector(cgi("tags"));
     transform(entry.tags.begin(), entry.tags.end(), entry.tags.begin(),
@@ -184,9 +192,24 @@ string text2html(string text)
     return text;
 }
 
+bool captcha_valid(std::uint8_t id, const string_view answer)
+{
+    std::array<string, 6> answers{"2", "6", "17", "12", "4", "1"};
+    if (answers.at(id) == answer)
+    {
+        return true;
+    }
+    return false;
+}
+
 } // namespace FediBlock::cgi
 
 const char *SpamException::what() const noexcept
 {
     return "Spam detected.";
 }
+
+const char *CaptchaException::what() const noexcept
+{
+    return "The solution to the captcha is not correct.";
+}

src/cgi.hpp

@@ -19,6 +19,7 @@
 
 #include "types.hpp"
 
+#include <cstdint>
 #include <exception>
 #include <string>
 #include <string_view>
@@ -52,6 +53,9 @@ using std::vector;
 // Replace certain characters with HTML tags or entities.
 string text2html(string text);
 
+// Check if the answer matches the solution we have for the id.
+bool captcha_valid(std::uint8_t id, string_view answer);
+
 } // namespace FediBlock::cgi
 
 class SpamException : public std::exception
@@ -61,4 +65,11 @@ public:
     const char *what() const noexcept override;
 };
 
+class CaptchaException : public std::exception
+{
+public:
+    // NOLINTNEXTLINE(modernize-use-nodiscard)
+    const char *what() const noexcept override;
+};
+
 #endif // FEDIBLOCK_BACKEND_CGI_HPP

src/main.cpp

@@ -84,6 +84,12 @@ int main()
         cerr << e.what() << '\n';
         cout << e.what() << "\r\n";
     }
+    catch (const CaptchaException &e)
+    {
+        cerr << e.what() << '\n';
+        cout << e.what() << "\r\n"
+             << "Use the back button of your browser to try again.\r\n";
+    }
     catch (const exception &e)
     {
         cerr << e.what() << '\n';